Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of that shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The common shaft extending between the turbine and compressor is disposed through a turbocharger center housing that includes a bearing assembly for: (1) facilitating shaft rotation (2) controlling axially directed shaft thrust effects and radially direct shaft vibrations; (3) providing necessary lubrication to the rotating shaft to minimize friction effects and related wear; and (4) providing a seal between the lubricated assembly and the turbine and compressor housings.
Because the rotary action of the turbine is dependent upon the heat and volumetric flow of exhaust gas exiting the engine, turbochargers are often of reduced effectiveness when the engine to which they are coupled is run at a low speed. The reduced effectiveness is often labeled turbo-lag. In order to overcome turbo-lag during operating conditions when the heat and volumetric flow of exhaust gas is low, an electric motor can be used to rotate the shaft and induce the compressor to spin at high speed.
An electric assisted turbocharger is capable of spinning at high speeds when the associated engine is running at very low speeds, or not running at all. During these operating conditions it is very possible that the pressure and flow of lubricating oil to the turbocharger bearing will be insufficient. Insufficient oil flow during high speed electric assisted operation of turbocharger may cause permanent damage to the bearing system. Therefore, it is desirable that a system be devised for detecting/monitoring the flow of lubricating oil to the turbocharger bearing, and for preventing and/or controlling the spinning of the turbocharger shaft when the monitored oil pressure and flow are inadequate.